The present invention relates generally to processes for continuously casting thin steel strip, and more specifically to systems for determining casting roll operating temperature and controlling one or more thin strip casting process parameters as a function thereof.
It is known to cast metal strip by continuous casting in a twin roll caster. In such a process, molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product which is delivered downwardly from-the nip between the rolls. The molten metal may be introduced into the nip between the two rolls via a tundish and a metal delivery nozzle system located beneath the tundish so as to receive a flow of metal from the tundish and to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip. This casting pool may be confined between side plates or dams held in engagement with end surfaces of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed for this purpose.
When casting thin steel strip in a twin roll caster of the type just described, the molten steel in the casting pool will generally be at a temperature of the order of 1500xc2x0 C. and above, and very high cooling rates are achieved over the surfaces of the casting rolls. To this end, the casting rolls are typically liquid cooled uniformly adjacent to their surfaces in order to promote rapid solidification of the thin metal strip. In the twin roll casting process, care must be taken to avoid excessive casting roll surface temperatures that may cause accelerated deterioration of the casting rolls, potentially leading to catastrophic explosions caused by leakage of the cooling liquid into the casting pool. Control of the surface temperature of the casting rolls is therefore critical to this thin strip casting process.
A primary obstacle to the successful control of casting roll surface temperature has been the difficulty in accurately measuring or estimating the surface or operating temperature of the casting rolls. Typical casting roll temperatures are of the order of 360xc2x0 C. and above, and it is impractical to measure this temperature using currently available temperature sensors. Known techniques for estimating casting roll temperature, on the other hand, are bulky and not easily implemented with a computerized control system to provide on-line, instantaneous casting roll temperature information.
What is needed is a casting roll operating temperature determination system that is easily implemented in software and that accurately bases the casting roll operating temperature determination on easily measured operating conditions. Such a system would allow for on-line, real-time monitoring of casting roll operating temperature, and further provide a platform to implement casting roll operating temperature-based prognostic and diagnostic capabilities.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a method is provided comprising the steps of determining an inlet temperature (TI) and an outlet temperature (TO) of cooling liquid circulated through a cooling system of the at least one casting roll, computing a heat flux value (Q) as a function of the inlet and outlet temperatures, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and computing the surface temperature of the at least one casting roll (TROLL) as a function of the heat flux value and the outlet temperature.
In accordance with another aspect of the present invention, a system is provided comprising a first temperature sensor producing a first temperature signal (TI) indicative of temperature of cooling liquid entering a cooling system of the at least one casting roll, a second temperature sensor producing a second temperature signal (TO) indicative of temperature of cooling liquid exiting the cooling system of the at least one casting roll, and a computer computing a heat flux value (Q) as a function of said first and second temperature signals, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and computing the surface temperature of the at least one casting roll (TROLL) as a function of said second temperature signal and said heat flux value.
In accordance with a further aspect of the present invention, a method is provided comprising the steps of determining an inlet temperature (TI) and an outlet temperature (TO) of cooling liquid circulated through a cooling system of the at least one casting roll, computing a heat flux value (Q) as a function of the inlet and outlet temperatures, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, developing a correlation between the surface temperature of the at least one casting roll (TROLL), the heat flux value and the outlet temperature, mapping a first threshold surface temperature to a first threshold outlet temperature using the correlation, monitoring the outlet temperature, and generating a signal if the outlet temperature exceeds the threshold outlet temperature, the signal thereby indicative of the surface temperature of the at least one casting roll exceeding the first threshold surface temperature.
In accordance with yet another aspect of the present invention, a system is provided comprising a first temperature sensor producing a first temperature signal (TI) indicative of temperature of cooling liquid entering a cooling system of the at least one casting roll, a second temperature sensor producing a second temperature signal (TO) indicative of temperature of cooling liquid exiting the cooling system of the at least one casting roll, and a computer computing a heat flux value (Q) as a function of said first and second temperature signals, the heat flux value indicative of an amount of heat removed from the at least one casting roll by the cooling system, and correlating the surface temperature of the at least one casting roll (TROLL) to the heat flux value and the second temperature signal, said computer mapping a first threshold surface temperature to a first threshold outlet temperature using the correlation and generating a control signal if the second temperature signal exceeds the threshold outlet temperature, the control signal thereby indicative of the surface temperature
The present invention provides a model-based system for determining casting roll operating temperature in a thin strip casting process.
The present invention also provides a thin strip casting control system for modifying one or more operating parameters associated with the steel casting process as a function of the casting roll operating temperature.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.